The invention pertains to methods of forming layers over substrates. In particular aspects, the invention pertains to methods of forming trenched isolation regions.
There are numerous applications in which it is desired to form layers over substrates. For instance, it is frequently desired to form layers over semiconductor constructions during fabrication of integrated circuitry. Among the methods commonly utilized for layer formation are chemical vapor deposition (CVD) processes and atomic layer deposition (ALD) processes. A problem which can occur with CVD processes is that there is frequently less than 100% step coverage. For instance, if CVD is utilized to form a plug of material within a trench, there will frequently be a void present within the plug. The void forms because the deposition rate at the neck (top) of the trench is higher than that on the sidewall, and accordingly the entrance to the trench becomes pinched off by the depositing film before the trench is completely filled with the film.
ALD generally has better step coverage than CVD, and in some cases can come very close to, or even achieve, a voidless fill process. However, ALD can be slow, and (barring certain special cases, such as the catalytic ALD of SiO2 using tetramethylaluminum and tris(tert-butoxy)silanol) the growth rates are typically on the order of about 1 xc3x85 per cycle.
Recently, it has been proposed to utilize supercritical fluids to deliver precursors to a surface during formation of layers. A frequently utilized supercritical fluid consists essentially of, or consists of CO2.
The supercritical fluids are known to be exceptional solvents. The supercritical fluids are typically utilized by first providing a precursor within the supercritical fluid at high concentration, thus taking advantage of the solvent characteristics of the supercritical fluid. The supercritical fluid having the precursor dissolved therein is provided within a reaction chamber proximate to a substrate. Subsequently, the temperature and/or pressure conditions within the chamber are reduced so that the fluid is changed to a non-supercritical state. The fluid then lacks the solvent properties which can keep the precursor in solution, and accordingly the precursor falls out of solution and forms a layer (or a film) over the substrate.
Although supercritical fluid techniques can have advantages relative to ALD and CVD practices, there remains a need for improved methods of forming layers over substrates, and particularly for improved methods for forming layers over semiconductor substrates.
In one aspect, the invention pertains to a method of forming a layer of material on a substrate. A substrate is provided within a reaction chamber, and a mixture is also provided within the chamber. The mixture comprises a precursor of a desired material within a supercritical fluid, and is initially provided in the chamber under first conditions at which the precursor is stable. Subsequently, and while maintaining the supercritical state of the supercritical fluid, the conditions within the reaction chamber are changed to second conditions under which the stability of the precursor is altered relative to the first conditions. The precursor reacts under the second conditions to form the desired material, and at least some of the desired material forms a layer on the substrate. A difference between the first conditions and the second conditions can be, for example, that the second conditions comprise a higher temperature than the first conditions.
In one aspect, the invention pertains to a method of forming at least one trenched isolation region. A semiconductor substrate is provided within a reaction chamber, and the substrate has at least one trench extending therein. A mixture is provided within the chamber, with the mixture comprising a precursor of an electrically insulative material dissolved within a supercritical fluid. The precursor is reactive above at or above a threshold temperature to form the electrically insulative material. The mixture is initially provided within the reaction chamber at a temperature below the threshold temperature. Subsequently, the temperature of the mixture is raised to a temperature at or above the threshold temperature to form the electrically insulative material within at least one trench.